<opus-link>

<opus version="4.0"> <title>Fidelio</title> <opus-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="Aufzug1.musicxml"/> <opus-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="Aufzug2.musicxml"/> </opus>